Definitely helpful Wes. The S-meter cal is a whole separate process, right? Do I need to do that again?
My ears, as well as the meter tell me I'm not hearing as much junk. Meaning external noise, not internal. 73, Mike Wes Stewart wrote: > Maybe some clarification of what the "calibration" really does would be > helpful. > > The hardware AGC in the K3 operates on the post-filter FET IF amplifier and > associated diodes. The "RF" gain control (really IF gain) under the control > of the DSP adds a control voltage to the hardware AGC loop. If the manual > gain control voltage exceeds the detected AGC voltage then it controls the IF > gain, otherwise, it's in the hands of the AGC detector. > > Unfortunately, there is variability (no pun intended) in the FET Gm, from > device to device, hence for a given control voltage, each FET behaves > differently. In comparison of my K3 to another, the differences were > remarkable. In mine, even a slight reduction of manual gain caused an > immediate and obvious degradation of SNR even on a BC station that was S9+50 > dB. The comparison radio was much better behaved. > > Anyone who has done any design work on receivers understands "delayed" AGC > where the delay serves to keep the gain nearer the front end high enough to > maintain SNR and only reduces it after the SNR is fully developed. Clearly, > in my radio's case, the gain partitioning between the IF and DSP was being > negatively affected and the SNR took a hit. > > The RF gain calibration was a response to this issue and serves to measure > the dB gain reduction vs. control voltage and develop a correction in > firmware that linearizes (in dB) the curve. > > Contrary to the belief of some, this isn't an S-meter calibration, although > that is a secondary benefit. Likewise, absent the development of hardware > AGC and/or the manual reduction of IF gain, it doesn't change the overall > gain of the radio. > > > > --- On Sun, 3/14/10, r...@aol.com <r...@aol.com> wrote: > > >> From: r...@aol.com <r...@aol.com> >> Subject: [Elecraft] K-3 RF Gain Calibration >> To: elecraft@mailman.qth.net >> Date: Sunday, March 14, 2010, 12:22 PM >> Mike, >> >> Are you saying that your S-Meter reads 3-4 s-units MORE >> noise level now >> that you did the RF Gain calibration with the XG-2? I >> was going to make the >> same adjustment with my K-3. But if you are getting a >> 3-4 s-unit higher >> noise level after the adjustment has been done... I won't >> be making the >> adjustment as my K-3 is already more sensitive than I need >> on the low bands. >> I'd use a 20dB ATT on the low bands often if I had >> one available. Perhaps >> one day we'll be able to change the K-3's RF Gain per >> band via software to >> help adapt to our local noise environment. >> (mine is very noisy on the low >> bands with thunderstorm QRN off the Atlantic). >> For those who may be >> concerned, yes I do use the RF Gain control. >> >> 73, >> Dick- K9OM >> >> >> Sorry if this comes across more than once, I'm having some >> e-mail issues. >> >> I just did an RF gain calibration, using the XG2 and the >> K3 utility on >> my kit K3 (built in Sept. '09). >> >> There seems to be a dramatic difference in my noise >> level, 3-4 s units, >> with a calibrated s-meter. I think I can pull more >> stuff out of the >> ditches and weeds now. >> >> Does that seem reasonable? >> >> 73, Mike NF4L >> >> ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
